The present invention relates generally to a computer-generated hologram, and more particularly to a computer-generated hologram suitable for use as a reflector and its fabrication process as well as a reflective liquid crystal display using a computer-generated hologram.
Of a variety of display systems already put to practical use, liquid crystal display systems have now wide applications because they have some advantages of low power consumption, color display capability, low-profile size, and low weight.
Instead of LCDs, it is difficult to use other type of displays for terminal equipment having no other choice to rely on batteries or accumulators.
However, LCDs cannot emit light by themselves; in other words, extraneous light or illumination light is necessary for viewing images irrespective of whether they are of the reflection type or the transmission type.
However, the use of sufficiently bright illumination light goes against the valuable advantage of low power consumption. Accordingly, even when illumination light is used, it is unreasonable to make use of illumination having relatively high illuminance; whether the light used is extraneous light or illumination light, how limited light is effectively used is of vital importance.
The applicant has already filed patent applications (JP-A""s 11-296054 and 11-183716) to come up with computer-generated holograms having a phase distribution capable of diffracting obliquely incident light in a predetermined viewing region. Of both, JP-A 11-296054 discloses a computer-generated hologram having a phase distribution for allowing light incident thereon at an oblique angle of incidence to be diffracted into the predetermined viewing region.
To fabricate these computer-generated holograms which are still found to have the desired effects, however, it is required to use a time-consuming, inefficient fabrication process comprising the steps of using a computer to find phase distributions all over the hologram region by computations, and making a relief pattern for the replication of computer-generated holograms on the basis of computation results.
For photoetching in particular, it is preferable to make use of a photomask fabrication system because precise exposure is needed. However, the photomask fabrication system has some disadvantages of high cost, severe fabrication conditions and extended fabrication time, in which the extended fabrication time in particular offers a grave problem.
One object of the present invention is to provide a novel computer-generated hologram which can be viewed in white at the desired viewing region, and a reflective liquid crystal display using the same as a reflector.
Another object of the present invention is to eliminate a problem in association with the fabrication of a relief pattern for computer-generated hologram fabrication, and especially a time problem in connection with data processing on aligners for photoetching.
Throughout the present disclosure, the term xe2x80x9cphotoetchingxe2x80x9d is understood to mean a photostep for providing the desired pattern to a photosensitive material by means of laser light, electron beams or the like and etching the pattern into a relief configuration.
Yet another object of the present invention is to provide a computer-generated hologram which has improved optical diffraction efficiency, allows a master pattern to be easily obtained for replication purposes, is easy to fabricate, and enables its relief surface to come into contact with the back surface of a light transmission display device as well as a reflective liquid crystal display using the same as a reflector.
According to the first invention to achieve the aforesaid first object, there is provided a computer-generated hologram designed to diffuse light having a given reference wavelength and incident thereon at a given angle of incidence in a specific angle range, characterized in that, in a range of wavelengths including said reference wavelength wherein zero-order transmission light or zero-order reflection light incident on said computer-generated hologram at a given angle of incidence is seen in white by additive color mixing, the maximum diffraction angle of incident light of the minimum wavelength in said range and incident at said angle of incidence is larger than the minimum diffraction angle of incident light of the maximum wavelength in said range and incident at said angle of incidence.
Preferably in this case, the computer-generated hologram comprises an array of two-dimensionally arranged minute cells, wherein each cell has an optical path length for imparting a unique phase to reflection light or transmission light, and a phase distribution obtained by adding a first phase distribution that substantially diffracts a vertically incident light beam within a given viewing region and does not substantially diffract the light beam toward other region to a second phase distribution that allows an obliquely incident light beam at a given angle of incidence to leave the cell vertically.
Alternatively, the computer-generated hologram may comprise an array of two-dimensionally arranged minute cells, wherein each cell has an optical path length for imparting a unique phase to reflection light or transmission light as well as a phase distribution which substantially diffracts an obliquely incident light beam at a given angle of incidence within a given viewing region and does not substantially diffract the light beam toward other region and which substantially diffracts a vertically incident light beam within another region shifted from said given viewing region and does not substantially diffract the light beam toward a region except for said another region.
Practically, the cells are arranged in columns and rows just like checkers.
Further, the computer-generated hologram may be a reflection computer-generated hologram wherein a reflective layer is provided on a relief pattern provided on the surface of the substrate.
Further, the computer-generated hologram may be constructed in such a way as to be adaptable to the minimum wavelength of 450 nm and the maximum wavelength of 650 nm.
Preferably, the computer-generated hologram should satisfy:
xcexMIN/xcexMAXxe2x89xa7(sin xcex21STDxe2x88x92sin xcex8)/(sin xcex22STDxe2x88x92sin xcex8)xe2x80x83xe2x80x83(11) 
where xcex8 is the angle of incidence of illumination light, xcexMIN is the minimum wavelength, xcexMAX is the maximum wavelength, xcex21STD is the minimum diffraction angle at a given reference wavelength xcexSTD and xcex22STD is the maximum diffraction angle at the given reference wavelength xcexSTD. 
It is also preferable that the computer-generated hologram satisfies:
sin xcex8xe2x89xa7(xcexMAX sin xcex21STDxe2x88x92xcexMIN sin xcex22STD)/(xcexMAXxe2x88x92xcexMIN)xe2x80x83xe2x80x83(12) 
where xcex8 is the angle of incidence of illumination light, xcexMIN is the minimum wavelength, xcexMAX is the maximum wavelength, xcex21STD is the minimum diffraction angle at a given reference wavelength xcexSTD and xcex22STD is the maximum diffraction angle at the given reference wavelength xcexSTD.
A display system of the invention is characterized by using any one of the aforesaid computer-generated holograms as a reflector.
One reflective liquid crystal display system of the invention is characterized in that any one of the aforesaid computer-generated holograms is disposed as a reflector on the back surface thereof.
Another reflective liquid crystal display system of the invention is characterized in that any one of the aforesaid computer-generated holograms is interposed as a reflector between a liquid crystal layer thereof and a back surface substrate thereof.
According to the invention to achieve the aforesaid first object, the computer-generated hologram is constructed such that, in a range of wavelengths including the reference wavelength wherein zero-order transmission light or zero-order reflection light incident on the computer-generated hologram at a given angle of incidence is seen in white by additive color mixing, the maximum diffraction angle of incident light of the minimum wavelength in said range and incident at said angle of incidence is larger than the minimum diffraction angle of incident light of the maximum wavelength in said range and incident at said angle of incidence. Thus, the computer-generated hologram can be seen in white in the angle range defined between the maximum diffraction angle of the minimum wavelength and the minimum diffraction angle of the maximum wavelength, and there is no change in the color seen even when the viewer moves his eyes within that range. This computer-generated hologram is suitable for reflector in reflective LCDs.
In one typical process for the fabrication of computer-generated holograms used so far in the art, phase distributions are calculated all over the region of the hologram to be fabricated. Then, a large amount of data are entered into an aligner on the basis of the results of calculations for exposure processing. According to the invention provided to achieve the aforesaid second object, a computer-generated hologram is constructed of an array of minute elemental hologram pieces arranged in columns and rows. Then, the calculation of the phase distribution is performed only for the minute elemental hologram piece by far smaller than the entire computer-generated hologram. When exposure is carried out for photoetching, too, a much smaller amount of data on the minute elemental hologram piece than before are used, so that loads on the data processing on the aligner can be alleviated to reduce the overall exposure time. Thus, the twelfth invention provided to achieve the second object has been accomplished.
That is, the twelfth invention provided to achieve the second object relates to a computer-generated hologram comprising minute elemental hologram pieces closely arranged on a plane, characterized in that each elemental hologram piece has an optical path length enough to impart an identical phase distribution to reflection light or transmission light.
The thirteenth invention provided to achieve the second object and according to the twelfth invention relates to a computer-generated hologram designed to diffuse light having a given reference wavelength and incident thereon at a given angle of incidence in a specific angle range, characterized in that, in a range of wavelengths including said reference wavelength wherein zero-order transmission light or zero-order reflection light incident on said computer-generated hologram at a given angle of incidence is seen in white by additive color mixing, the maximum diffraction angle of incident light of the minimum wavelength in said range and incident at said angle of incidence is larger than the minimum diffraction angle of incident light of the maximum wavelength in said range and incident at said angle of incidence.
The fourteenth invention provided to achieve the second object and according to the twelfth or thirteenth invention relates to a computer-generated hologram, characterized in that each elemental hologram piece has a phase distribution obtained by adding a first phase distribution that substantially diffracts a vertically incident light beam within a given viewing region and does not substantially diffract the light beam toward other region to a second phase distribution that allows an obliquely incident light beam at given angle of incidence to leave the elemental hologram piece vertically.
The fifteenth invention provided to achieve the second object and according to the twelfth or thirteenth invention relates to a computer-generated hologram, characterized in that each elemental hologram piece a phase distribution which substantially diffracts an obliquely incident light beam at a given angle of incidence within a given viewing region and does not substantially diffract the light beam toward other region and which substantially diffracts a vertically incident light beam within another region shifted from said given viewing region and does not substantially diffract the light beam toward a region except for said another region.
The sixteenth invention provided to achieve the second object is characterized in that the computer-generated hologram according to any one of the aforesaid twelfth to fifteenth inventions comprises a resin layer including a hologram.
The seventeenth invention provided to achieve the second object is characterized in that the computer-generated hologram according to the aforesaid sixteenth invention further comprises a transparent substrate for supporting the resin layer including a hologram.
The eighteenth invention provided to achieve the second object is characterized in that the computer-generated hologram according to any one of the aforesaid twelfth to seventeenth inventions is defined by a relief pattern on the surface of a hologram-forming layer.
The nineteenth invention provided to achieve the second object is characterized in that the computer-generated hologram according to the aforesaid eighteenth invention further comprises an optical reflective layer laminated on and along said relief pattern.
The 20th invention provided to achieve the second object is characterized in that in the aforesaid 18th invention, said optical reflective layer is laminated on the other bare surface of said hologram-forming layer which is free from said relief pattern.
The 21th invention provided to achieve the second object relates to a reflector characterized by using the computer-generated hologram according to any one of the aforesaid 12th to 20th inventions.
The 22nd invention provided to achieve the second object relates to a reflective liquid crystal display characterized in that the computer-generated hologram according to claim 10 is disposed on a back surface thereof.
The 23rd invention provided to achieve the second object relates to a reflective liquid crystal display characterized in that the computer-generated hologram according to the aforesaid 21st invention is interposed between a liquid crystal layer and a back substrate in said liquid crystal display.
The 24th invention provided to achieve the second object relates to a computer-generated hologram fabrication process characterized by defining a range which diffraction light obtained by diffraction of incident light leaves, determining a hologram phase distribution for allowing said diffraction light to leave the defined range, quantizing the determined phase distribution to find a quantized depth of a hologram relief, forming a relief on a substrate by photoetching on the basis of the found quantized depth to obtain a relief pattern, and patterning a resin layer using said relief pattern to form a hologram relief on the surface of said resin layer.
The 25th invention provided to achieve the second object relates to a computer-generated hologram fabrication process characterized by defining a range which diffraction light obtained by diffraction of incident light leaves, determining a hologram phase distribution for allowing said diffraction light to leave the defined range, quantizing the determined phase distribution to find a quantized depth of a hologram relief and the number of steps of said depth, repeating photoetching given times corresponding to the obtained depth and the number of steps to form a relief pattern on an etching substrate, and patterning a resin layer using said relief pattern to form a hologram relief on the surface of said resin layer.
The 26th invention provided to achieve the second object relates to the computer-generated hologram fabrication process according to the aforesaid 24th or 25th invention, characterized in that said phase distribution is determined per minute elemental hologram piece forming the hologram, and said relief is formed on the basis of a phase distribution obtained by repeatedly arranging a phase distribution of said elemental hologram piece in a longitudinal direction of said substrate.
The 27th invention provided to achieve the second object relates to the computer-generated hologram fabrication process according to any one of the aforesaid 24 to 26th inventions, characterized in that an optical reflective layer is laminated on and along a relief side or other side of said resin layer.
The 28th invention provided to achieve the second object relates to the computer-generated hologram fabrication process according to any one of the aforesaid 24th to 26th inventions, characterized in that the number of steps L having the depth of said relief is the N-th power of 2 where N is the number of photoetching cycles.
Reference is then made to a computer-generated hologram constructed to achieve the aforesaid third object of the present invention. This computer-generated hologram comprises a transparent plate material having a light refractive index higher than that of air and a blaze pattern of sawtoothed shape in section, which blaze pattern is disposed on the back surface of the transparent plate, and is designed in such a way that the depth d of the blaze is equivalent to a half wavelength or d=xcex/2n wherein xcex is the wavelength of reference light and n is the light refractive index of the transparent plate. This computer-generated hologram can provide solutions to prior art problems in conjunction with diffraction efficiency, master pattern fabrication and replication and applications. Thus, the present invention provides such a computer-generated hologram as well as a reflector and a reflective LCD constructed using the same.
The 29th invention provided to achieve the third object relates to a computer-generated hologram characterized in that a blaze pattern of sawtoothed shape in section is formed on a back side of a transparent substrate and the depth d of said blaze pattern is d=xcex/2n where xcex is the wavelength of reference light and n is the light refractive index of a material forming said transparent plate.
The 30th invention provided to achieve the third object relates to a computer-generated hologram characterized in that a blaze pattern of sawtoothed shape in section is formed on a back side of a transparent substrate with N steps having differences in level and the depth d of said blaze pattern is d=xcex/2n where xcex is the wavelength of reference light and n is the light refractive index of a material forming said transparent plate.
The 31st invention provided to achieve the third object relates to the computer-generated hologram according to the aforesaid 29th or 30th invention, characterized in that an optical reflective layer is laminated on and along said blaze pattern formed on the back surface of said transparent plate.
The 32nd invention provided to achieve the third object relates to the computer-generated hologram according to any one of the aforesaid 29th to 31st inventions, characterized in that the front surface of said transparent plate has been subject to antireflection treatment.
The 33rd invention provided to achieve the third object relates to a reflector characterized by using the computer-generated hologram according to any one of the aforesaid 29th to 32nd inventions.
The 34th invention provided to achieve the third object relate to the reflector according to the aforesaid 33rd invention, characterized in that a transparent adhesive layer is laminated on the front surface of said transparent plate.
The 35th invention provided to achieve the third object relates to a reflective liquid crystal display characterized in that said front surface of the reflector according to the aforesaid 33rd invention is in close contact with the back surface of said liquid crystal display.
The 36th invention provided to achieve the third object relates to a reflective liquid crystal display characterized in that said front surface of the reflector according to the aforesaid 34th invention is laminated on the back surface of said liquid crystal display with said transparent adhesive layer interposed therebetween.
The 37th invention provided to achieve the third object relates to the reflective liquid crystal display according to the aforesaid 35th or 36th invention, characterized in that a liquid crystal display device and said transparent plate in said reflector have a substantially identical light refractive index, or said liquid crystal display device, said transparent adhesive layer and said transparent plate in said reflector have a substantially identical light refractive index.
The 38th invention provided to achieve the third object relates to a reflective liquid crystal display characterized in that the computer-generated hologram according to the aforesaid 33rd invention is interposed between the liquid crystal layer and the back substrate in said liquid crystal display with the front surface of said computer-generated hologram opposite to said liquid crystal layer.
The 39th invention provided to achieve the third object relates to a reflective liquid crystal display characterized in that said front surface of the reflector according to the aforesaid 33rd invention is in close contact with the back surface of a light transmission display.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.